1978 Sedan de Ville warning lights

[My1stCadi]

Hello,
Recently purchased a 1978 Sedan de Ville with only 52,000 miles from an estate sale. It had been sitting about 2 years but with a fresh battery it fired right up. I checked the fluids, filled it with gas, and drove it 400 miles home with no problems. But I was working on it today and saw that the connector on the oil pressure switch was disconnected. But no warning lights are lit. Actually several of the warning lights do not light up even when I turn the key. The manual says that some should light up in the start position. The only lights I have lit are GENERATOR, BRAKES, and TRUNK OPEN. No other lights with the key in accessory or start position. All the fuses are good. Is this normal?

[Cadman-iac]

Your oil light should come on with the key before you start it. Once it is running of course it should go out.
The other lights you mentioned are correct,  but I believe that you should also get a temperature light with the key in the crank position. Im not positive what it should read, some say "engine temp stop engine" or something like that.
I would have to throw a battery in my 77 in order to tell you for sure what lights come on and what they say exactly.
However someone here has a running one and could tell you faster than I could.

[My1stCadi]

Ok. Since the oil pressure sensor is unplugged that should trigger an oil light. Right?

[TJ Hopland]

I think the oil light gets a ground to light the light so not having it connected would make it not light and maybe also explains why it doesn't come on with the key. 

The oil pressure switch is on the back of the block kinda where the distributor would be on a Chev. 

There are also 2 other sensors that non Cadillacs don't have, they look like a nut with one electrical tab.  There is one on the front corner of the head behind the alternator, this one when it trips sends a ground signal to the climate control which allows higher blower speeds in heat modes.  A Cadillac owner can't have cold air blowing on them so it stays on low till the engine has some heat in it. 

There is an identical looking sensor in the back corner head near the brake booster, this is the engine temp or maybe by 77 said something like stop temp.  Its different than the water coolant temp light and sensor which is under the AC compressor. 

[My1stCadi]

Ok. I’ve never had a vehicle that didn’t at least have a temp gauge. Just want to know that the lights are working before I drive it much more.

[Cadman-iac]

To answer your question, yes, the disconnected oil switch would cause the light not to come on at any time.
That switch is just a ground when there's no oil pressure, so when you first turn the key on, it is supposed to turn on the oil light.
Now when the engine is cranking, once the oil pressure is high enough to trip the switch,  the light will go out, even if the engine has not started yet.
Also,  the light is supposed to come on whenever the engine is not running, with the ignition switch in run or start positions.

[78Elegante]

I always like to see a schematic: http://www.cadillacseville.org/elctroubleshoot78.html#28
(scroll down to the second schematic).

This shows the last answer of Cadman-iac explains the working of the light and the switch correctly.

[Eric DeVirgilis CLC# 8621]

Reconnect the oil pressure switch and report back.

TRUNK OPEN lamp should not illuminate with the decklid latched shut under any circumstances.

[My1stCadi]

The Trunk Open light does come on only with the trunk open. I was listing the lights that are working and I should have specified that. I replaced the oil pressure switch and I hope I never have to do that again. The oil pressure light is working now. But the 2 coolant lights are still out and. Still troubleshooting and will let you know.

[The Tassie Devil(le)]

G'day Keith,

You should have received an email from the Moderators that requires your attention.

It was sent 3 days ago.

Bruce.

[My1stCadi]

After a lot of troubleshooting it was the ignition switch that needed to be replaced. It looks like it got a little hot at some point because the wires were pretty dark. Replaced it and all is well again. Thanks for all your input. I appreciate it! 

[TJ Hopland]

If the ignition switch got stressed I would be curious why and the condition of everything else in the path.  Everywhere before the ignition switch would also have to be stressed among those things the connector that feeds that in the bulkhead connector on the firewall.

Maybe have a look at the harness coming up from the starter which is where the fusible link wires are.  Maybe there was an issue there at some point in the past and they were not replaced with the correct wires and there are other issues or modifications causing the overload and there isn't that final level of protection of the correct fusible link wires.

[My1stCadi]

I’m curious as well. But it’s 42 years old and I’ve only owned it for a month. I used the shop manual to troubleshoot It. All I know is that after replacing the ignition switch all the telltale lights are working again, and the new ignition turns much easier compared to the old one.

[The Tassie Devil(le)]

G'day Keith,

You have an email from the Moderators that requires your attention,

Thanks,

Bruce.